In recent years, the rapid growth of the information industry has resulted in extensive consumption of large amounts of printing plates, photographic films and magnetic storage media, such as computer tapes, audio tapes, video tapes and floppy disks. In particular, magnetic tapes and floppy disks which have, for example, polyethylene terephthalate as the substrate have been produced in growing amounts in recent years, owing to their excellent magnetic and mechanical properties. In general, residues and wastes of such storage media occur in large amounts in the production and during use by the end users. At present, such wastes are disposed of by depositing them with the domestic waste in sanitary landfills or incinerating them in incineration furnaces. From the point of view of waste reduction and the recovery of useful materials, full utilization of such wastes is an outstanding requirement.
A process of the generic type stated at the outset is disclosed in DE-A 33 41 608. According to this publication, magnetic tape wastes are finely shredded, after which the magnetic layer and the substrate are delaminated in aqueous alkaline solution and the magnetic powder is then separated from the substrate by stirring at high speed. This process requires a very complicated bulky apparatus and a large amount of energy, since the treatment liquid must be heated to at least 90.degree. C.
Further processes which are based on separation of the magnetic layer from the substrate by treatment with a base are described in Japanese Patent Applications 112 979 (1978), 006 985 (1979), 070 404 (1978), 092 879 (1978) and 167 601 (1987) and Korean Patent Application 89/03614. Japanese Patent Applications 317 707 (1988), 112 413 (1989) and 146 624 (1982) describe separation by treatment with an acid. Japanese Patent Application 054 050 (1983) describes the use of a solvent mixture comprising phenol and tetrachloroethane for delamination of the magnetic layer.
U.S. Pat. No. 5,246,503 discloses a delamination solution for ink coatings which consists of organic solvent, water, thickener and wetting agent, where in addition the coating has to be removed mechanically by scratching.
If it is intended to delaminate the pigmented binder layer and the substrate and the aim is to recover the useful materials, in particular the pigment and the polyethylene terephthalate, the PET film should as far as possible not be chemically degraded or attacked. If, on the other hand, polyurethanes crosslinked in the magnetic layer are used, as described, for example, in European Patent 0,099,533, as binders, the processes described above are for the most part unsuccessful or give unsatisfactory results with regard to separation, delamination and recovery.
DE-A 43 30 889 of the same applicant describes a process for recovering raw materials from magnetic recording media, in which the latter in finely chopped form are treated in organic solvents, an acid which is soluble therein and alcohols or thioalcohols and, if required, surfactants at elevated temperatures, the magnetic layer delaminated in this manner being separated from the substrate by a washing process, and thereafter both the finely chopped substrate wastes and the magnetic powder being dried. The essential feature of this process is that the ester groups of the polyurethane binder are cleaved by hydrolysis by the stated treatment medium, whereas at the same time the ester groups of the polyethylene terephthalate substrate are not chemically destroyed. It has been found that it is difficult in this process to fulfil these boundary conditions; furthermore, the finely chopped wastes must be treated for many hours in order to achieve complete separation.
German Application DE-A 44 07 900 of the same applicant describes a process for recovery as in the abovementioned application, the finely chopped wastes being treated in a solution consisting of potassium salt of polyunsaturated fatty acids, one or more organic solvents and/or water with mechanical action and thereafter the detached magnetic powder being separated from the substrate by washing or settling out or in a magnetic separator. This process, too, requires the use of elevated temperatures in the range of 60-95.degree. C., can only be carried out as a batch process and thus does not permit relatively large amounts of coated films to be treated in an economically optimum manner.
JP-A-6238667 describes a continuous process in which the shredded magnetic tape wastes are divided into substrate film and magnetizable particles with the aid of a heated treatment solution, such as aqueous solutions of NaOH, surfactant-containing solutions, organic solvents or mixtures thereof The magnetic tape wastes are first transported in the separation kettle filled with treatment solution, stirred there for a few minutes and then fed to a mixer which accelerates the separation. Film particles and magnetizable particles are separated in a rotary sieve and the particles are filtered out of the treatment solution. The treatment solution purified in this manner is recycled to the separation kettle. This process likewise requires a great deal of energy since the treatment solution must be heated to 70-80.degree. C.
It is an object of the present invention to provide a process of the generic type stated at the outset and apparatus therefor, which process can be carried out at room temperature, the treatment solution being recovered and it being possible to recycle the raw materials from large amounts of coated films.